JP2010247118A - CODCr reduction method for high concentration silicone waste liquid - Google Patents

Abstract

Provided is a method for easily and stably reducing a high-concentration silicone waste liquid having COD _{Cr of} 500 mg / l or more to a level of COD _{Cr of} 100 mg / l or less.
SOLUTION: High concentration silicone waste liquid is subjected to pH adjustment, Fenton treatment, precipitation by increasing pH, coagulation precipitation treatment, activated sludge treatment, coagulation precipitation treatment in order, and finally activated carbon adsorption treatment, Reduce COD _Cr in silicone waste liquid.
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Description

The present invention relates to a method for reducing COD _Cr in a high concentration silicone waste liquid.

Various wastes are generated during the production of silicone monomers. This includes waste liquids containing silicone generated during the production of silicone monomers and each chlorosilane tank vent gas. The vent gas of chlorosilane generated in each chlorosilane production process is absorbed by hydrochloric acid gas with an alkali scrubber, but siloxane or silanol dissolved in waste water generated by hydrolysis of chlorosilane becomes a _CODCr object. This main component is trimethylsilane monool, dimethylsilanediol, methylsilanetriol, dimer, trimer or the like.

COD _Cr regulation is the decomposition hard silicone target, the main source is waste liquid containing a siloxane generated during manufacturing waste and dimethyldichlorosilane hydrolysis oils containing siloxane generated during methyl chloride production.

  This point will be described in more detail as follows.

Most of hydrochloric acid, which is a raw material of methyl chloride, reuses hydrochloric acid generated during oil production during hydrolysis of dimethyldichlorosilane. For this reason, low boiling point siloxane corresponding to the siloxane vapor pressure is accompanied with hydrochloric acid gas, and finally, it is contained in unreacted hydrochloric acid waste liquid and generated as waste water. Hydrochloric acid gas generation of dimethyldichlorosilane is operated at a considerably low temperature of about −10 ° C. due to endothermic reaction, but still contains 600 mg / l or more of COD _Cr component. Unreacted methanol is also recovered by distillation as much as possible after the reaction, but often remains.

If COD _Cr concentration regulating only the wastewater treatment is generally carried out, by performing the processing of the Fenton process such as attracting high COD _Cr silicone waste, it reduces the COD _Cr to a concentration of approximately half this waste liquid Can be diluted with low-concentration silicone waste liquid to clear the regulation value. However, there is a limit to the method of diluting with a low-concentration silicone waste liquid under the total amount regulation to which the water amount regulation is added.

  On the other hand, as one of the treatment methods for organic matter-containing wastewater, the Fenton method is known in which hydrogen peroxide and iron salt are added to decompose organic matter by Fenton reaction, and a method combined with activated carbon treatment is also proposed. (Patent Document 1).

However, in the conventional proposed method, it is difficult to _{COD Cr} 500 mg / l or more high density silicone waste reduced by simple and stable until COD _Cr 100 mg / l or less level.

JP-A-10-277568

An object of the present invention is to provide a method for easily and stably reducing a high-concentration silicone waste liquid having COD _{Cr of} 500 mg / l or more to a level of COD _{Cr of} 100 mg / l or less.

  As a result of intensive studies for achieving the above object, the present inventor has found that combining pretreatment including Fenton treatment and activated carbon adsorption treatment is extremely effective, and has completed the present invention.

That is, in the present invention, pH adjustment, Fenton treatment, precipitation by increasing pH, coagulation precipitation treatment, activated sludge treatment, coagulation precipitation treatment are sequentially performed on the high concentration silicone waste liquid, and finally the activated carbon adsorption treatment is performed. It is the COD _Cr reduction method of the high concentration silicone waste liquid characterized.

When the silicone monomer production waste liquid is shown as an index (COD _Cr ) that can be chemically decomposed with respect to the BOD value indicating the ease of biological treatment, the BOD ratio is as small as about 10%, and the waste water is very difficult to biologically treat. being classified.

Although silicone decomposition was attempted by hypochlorous acid treatment and ozone treatment, it was confirmed that the soluble silicone was very stable and did not decrease by 10% with COD _Cr . On the other hand, in Fenton treatment that generates hydroxyl radicals with the strongest oxidizing power, it is confirmed that it decomposes by 30 to 60% compared to COD _{Cr in} comparison with 10% or less of hypochlorous acid treatment and ozone treatment. It was.

The soluble silicone is a low molecular silicone having a polar group that also includes disilane, trisilane, and the like partially condensed with monosilane such as trimethylsilane monool, dimethylsilanediol, and methyltrisilanediol.
In addition to this, siloxane cyclics such as neutralized salts neutralized with hydrochloric acid, which dissolve only about 25 mg / l in ion-exchanged water, increase the solubility in water with neutralized salts.

In the COD _Cr reduction method of the high-concentration silicone waste liquid of the present invention, as pretreatment, pH adjustment, Fenton treatment, precipitation by increasing pH, aggregation precipitation treatment, activated sludge treatment, and aggregation precipitation treatment are sequentially performed.

There is no restriction | limiting in particular in each process of these pre-processing, The technique known conventionally can be applied.
(PH adjustment / Fenton treatment)
Generally, the high concentration silicone waste liquid has a pH of about 6 to 8 after the neutralization treatment. Hydrogen peroxide is stable and does not exhibit oxidizing power under acidic conditions, but when iron ions coexist, it generates hydroxy radicals based on the Fenton reaction and exhibits strong oxidizing power. In practice, when the pH is adjusted in the presence of these, specifically, when the pH is 4.5 or lower, preferably pH 2 to 4, hydroxy radicals are generated, and most organic substances and reducing substances are oxidized in an aqueous solution. Finally, it decomposes into carbon dioxide and water.
(Deposition / precipitation concentration treatment)
By increasing the pH to 10 to 11 after the Fenton treatment, Fe (OH) ₃ and Fe (OH) ₂ are precipitated as iron compounds and can be removed.
(Activated sludge treatment)
Activated sludge treatment has the property of adsorbing substances that are difficult to decompose, but COD by incorporating COD _Cr components through treatment of BOD components that have been decomposed and increased by Fenton treatment, electrolytic treatment, etc. and partial adsorption of components that are difficult to decompose There is an effect of reducing _Cr .

COD _Cr components include (1) methanol and dimethylsilanediol, which are polar components that are difficult to treat with activated carbon, (2) nonpolar (such as siloxane cyclics), and slightly polar water-soluble components (trimethylsilane monool, part of silanol) Condensates and the like). In addition, (3) inorganic substances such as nitrous acid (NO ₂ ) and ferrous hydroxide (Fe (OH) ₂ ) are also oxidized with potassium dichromate, and therefore indicate the number of COD _Cr . At least component (1) and component (3) are reduced by pretreatment, and component (2) is adsorbed and removed by activated carbon treatment. For example, it was confirmed that methanol that is easily decomposed decomposes 90% or more in the Fenton treatment, which is a pretreatment that has been shown to be effective as a chemical decomposition method. On the other hand, although there was concern about the increase in dimethylsilanediol, which is also a polar low molecule that is difficult to adsorb on activated carbon due to decomposition of water-soluble silicone, it was confirmed that it decreased by 60%. Methanol and dimethylsilanediol, which were difficult to adsorb, were initially 156 mg / l and 162 mg / l, respectively, but decreased to 11 mg / l and 57 mg / l, respectively. In terms of concentration, the total decreased from 318 mg / l to 68 mg / l. On the other hand, in terms of COD _Cr , it was reduced from 459 mg / l to 96 mg / l. The treatment liquid after the activated sludge treatment is divided into sludge and treatment liquid by adding a polymer flocculant and the like to coagulate and precipitate the sludge in a settling tank.

In this method, polar molecules that are difficult to adsorb on activated carbon are reduced as much as possible in the pretreatment step, and then the residual CODcr component is adsorbed by the activated carbon adsorption method. However, since the amount of granular activated carbon adsorbed is relatively small, it immediately exceeds COD _Cr 100 mg / l, so it has at least two series, semi-continuously or continuously treated granular activated carbon with hot water, steam. It is indispensable to perform desorption and drying regeneration.

Example 1
The COD _Cr of siloxane generated during the production of methyl chloride, which is the main source of COD _Cr, was measured and found to be 2500 mg / l. Residual methanol and dimethylsilanediol were initially present at 156 mg / l and 162 mg / l, respectively. When converted to COD _Cr , they were 234 mg / l and 225 mg / l, respectively, and were estimated to be 459 mg / l in total.

In order to reduce COD _Cr to 100 mg / l or less, it is necessary to reduce the above-mentioned two components that are difficult to adsorb on activated carbon to about 100 mg / l as a guide, and then pass through an activated carbon adsorption tower.

While 4 g of iron sulfate heptahydrate was added to 264 g of sample and stirred, 5 g of hydrogen peroxide and 10 g of hydrogen peroxide were added. When Fenton treatment was performed at pH 3 in the presence of these, it was confirmed that the COD _Cr component derived from methanol and dimethylsiloxane diol decreased to about 100 mg / l as a guide. Then, the treated water of COD _Cr 100 mg / l or less was obtained by passing through a granular activated carbon packed tower.

Example 2
The COD _Cr of the waste liquid mainly composed of siloxane generated during hydrolysis of dimethyldichlorosilane, which is the main source of COD _Cr , was 2150 mg / l. First, hydrogen peroxide and an iron salt were added, and Fenton treatment was performed at pH 3 in the presence of them, and after 4 hours, the COD _Cr decreased to 925 mg / l. Thereafter, the iron salt was sufficiently precipitated and separated by increasing the pH. Next, when activated sludge treatment was performed, COD _Cr decreased to 520 mg / l. Finally, the activated sludge coagulated and precipitated was removed by filtration with a filter paper, and passed through an activated carbon adsorption tower in which granular activated carbon was packed in a column. COD _{Cr was} 100 mg / l or less.
Data from the operation of Example 2 is shown in Table 1.

Claims (1)

High concentration silicone waste liquid is characterized by pH adjustment, Fenton treatment, precipitation by increasing pH, coagulation precipitation treatment, activated sludge treatment, coagulation precipitation treatment in order, and finally activated carbon adsorption treatment COD _Cr reduction method for silicone waste liquid.